Curable urethane resin composition

ABSTRACT

A curable urethane resin composition comprises a blocked urethane prepolymer which is prepared through condensation-polymerization of a polyol and an organic isocyanate and has a terminal isocyanate group protected by a blocking agent, and a polymer dispersed or dissolved in the blocked urethane prepolymer. The curable urethane resin composition may further comprise a crosslinking agent which performs crosslinking reaction with the terminal isocyanate group of the urethane prepolymer formed through deblocking of the blocked urethane prepolymer to make the prepolymer form a higher molecule while containing the polymer therein.

TECHNICAL FIELD

The present invention relates to a curable urethane resin compositionwhich is added into a coating material for use, for example, in coatingof a base material of a motor vehicle's body, for improving physicalproperties of the coating material, such as adhesiveness, flexibility,elongation characteristics, etc.

BACKGROUND ART

A pressed steel plate as the base material of a motor vehicle's body istreated with a sealer such as a sealing paint or a chipping resistantpaint to form a base layer on the surface thereof, and then over coatingis applied on the base layer.

As the sealer of this kind, a plastisol composition containing polyvinylchloride resin has been known as shown in Japanese Patent ProvisionalPublication No. 5-65450. The resulted coated layer has an excellentflexibility, elongation characteristics, tensile strength, flameresistance, adhesiveness, etc. which are peculiar to polyvinyl chloride.However it is feared that polyvinyl chloride might emit toxic substancessuch as hydrogen chloride, dioxin, etc. when burned.

As a safer sealer that contains no polyvinyl chloride, a compositioncontaining water-based emulsion resins, water-soluble resins, urethaneresins or acrylic resins has been studied. But excellent physicalproperties such as sealability, chipping resistance, adhesiveness, etc.have not so far been given to the coated layers, when compared topolyvinyl chloride resin-containing plastisol composition.

The present invention was made to solve the above mentioned problems.And an object of the present invention is to provide a curable andeasy-to-produce urethane resin composition which is used by adding intoa sealer, and gives excellent physical properties such as sealability,chipping resistance, flexibility, elongation characteristics, tensilestrength, adhesiveness, interfacial failure characteristics, etc. to thecoated layer made from the sealer, and to provide a heat-curableplastisol composition containing the curable urethane resin compositionwhich can be usable as a sealer.

DISCLOSURE OF INVENTION

The curable urethane resin composition aimed at achieving the abovementioned objects of the present invention comprises a blocked urethaneprepolymer which is prepared through condensation-polymerization of apolyol and an organic isocyanate and has a terminal isocyanate groupprotected by a blocking agent, and a polymer dispersed or dissolved inthe blocked urethane prepolymer.

Preferably, the curable urethane resin composition contains acrosslinking agent which performs crosslinking reaction with theterminal isocyanate group of the urethane prepolymer formed throughdeblocking of the blocked urethane prepolymer. The crosslinking agentperforms the crosslinking reaction to make the prepolymer form a highermolecule while containing the polymer therein.

The heat-curable plastisol composition for coating of the presentinvention comprises the curable urethane resin composition and finepowder of an acrylic resin.

When heated, the blocked urethane prepolymer splits thermally into theurethane prepolymer and the blocking agent. The urethane prepolymerscrosslink to each other under the presence of the terminal isocyanategroups, polymerizing into a higher molecule to form an urethane network.The polymer is embraced into and contained in the network.

Accordingly, when the coating material containing the heat curableplastisol comprising the urethane resin composition and the fine powderof the acrylic resin is heated, the coating material becomes hard toform a coated layer, while the polymer such as acrylic resin, which iscontained in the urethane network, and the fine powder are dissolved,entangled and strongly interacted with each other. As the result, thethus obtained coated layer has an excellent flexibility, elongationcharacteristics, tensile strength, flame resistance and adhesiveness.Further, the coated layer has an excellent repetitive abrasionresistance. Furthermore, excellent properties of the coated layer can berealized even if considerable amount of the fine powder of the acrylicresin in the plastisol composition is reduced.

EMBODIMENT OF INVENTION

The curable urethane resin composition of the present invention will bedescribed in detail hereunder.

The resin composition comprises a polymer dispersed or dissolveduniformly in a blocked urethane prepolymer, and a crosslinking agent ifnecessary.

A blocking agent, which forms the blocked urethane prepolymer, ispreferably at least one kind selected from oximes, secondary amines,phenols, alcohols and hydroxyl group-containing (meth)acrylic acidesters. More precisely, as oximes, aldoximes such as acetoxime,ketoximes such as methyl ethyl ketoxime, methyl isobutyl ketoxime, etc.can be exemplified. As secondary amines, secondary alkylamines such asdibutylamine, dicyclohexylamine, diisobutylamine, di-n-octylamine,di-2-ethylhexylamine, etc. can be exemplified. As phenols, alkylphenols,hydroxybenzoic esters, etc. and as alcohols, alkylalcohols can beexemplified. As hydroxyl group-containing (meth)acrylic acid esters,beta-hydroxypropyl (meth)acrylate, beta-hydroxyethyl (meth)acrylate suchas LIGHT-ESTER (trade name by Kyoeisha Chemical Co., Ltd.), epoxy esterssuch as EPOLIGHT (trade name by Kyoeisya Chemical Co., Ltd.) can beexemplified.

The blocking agent is optionally selected in view of the type of organicisocyanates which form the urethane prepolymer, or the temperature of aheat process at the time of forming a coated layer of the plastisolcomposition for coating containing the curable urethane resincomposition. Of which, methyl ethyl ketoxime or dicyclohexylamine ismore preferable.

Polyols which form the urethane prepolymer are polyether polyols. Aspolyether polyols, adducts produced from alkylene oxides having 2 to 6carbon atoms and low molecular weight compounds having 2 to 5 activehydrogen-containing functional group such as low molecular weightalcohols, low molecular weight amines, phenols, etc. are exemplified.

As such low molecular weight alcohols, ethylene glycol, propyleneglycol, diethylene glycol, dipropylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, trimethylolpropane, glycerin,diglycerin, castor oil and derivatives thereof are preferably used.Especially, neopentyl glycol, glycerin and diglycerin are morepreferable. As low molecular weight amines, alkanolamines such asmonoethanolamine, diethanolamine, triethanolamine, etc.; aliphaticpolyamines such as ethylenediamine, diethylenetriamine,triethylenetetramine, etc.; n-alkyl group substituted products of thesealiphatic polyamines; allyl group substituted products of thesealiphatic polyamines; n-alkyl group substituted products of aromaticpolyamines such as tolylenediamine, allyl group substituted products ofaromatic polyamines; heterocyclic polyamines such as piperidine,N-aminoethylpiperidine, etc.; alkylene oxide adducts of aliphaticpolyamines such as ethylenediamine, diethylenetriamine,triethylenetetramine, etc. are preferable. Especially, adducts producedfrom one equivalent of aliphatic polyamines to 0.1-16 equivalents ofpropylene oxide are more preferable. The low molecular weight amines maybe used as a mixture thereof. As phenols, catechol, resorcin,hydroquinone and bisphenol are preferable. As alkylene oxides, eitherone of ethylene oxide, propylene oxide and butylene oxide or a mixtureof two or more of them are preferable, and a mixture containing not lessthan 50% by weight of propylene oxide is more preferable. When themixture of two or more kinds of alkylene oxides is used, a random- orblock-polymerized polyol produced by reacting with low molecular weightcompounds such as low molecular weight polyols, etc. is obtained.

Polyols which form the urethane prepolymer may be polyester polyols. Asthe polyester polyols, polyester polyols prepared throughpolycondensation reaction using either one of dicarboxylic acidderivatives of dicarboxylic acids, dicarboxylic esters and dicarboxylichalides and low molecular weight polyols such as glycerine, diglycerine,propyleneglicol, etc., preferably glycerine or diglycerine; polyadductsprepared through polyaddition of the dicarboxylic acid derivatives toalkylene oxides; polylactone polyol esters prepared through ring openingpolymerization of lactones such as epsilon-caprolactone,delta-valerolactone, etc. and the low molecular weight polyols; areexemplified. As the dicarboxylic acids, aliphatic dicarboxylic acidssuch as adipic acid, sebacic acid, maleic acid, dimer acid, etc. or acidanhydrides thereof; aromatic dicarboxylic acids such as terephthalicacid, isophthalic acid, etc. or acid anhydrides thereof; are preferablyused. Aliphatic dicarboxylic acids are more preferable, and especiallyadipic acid is still more preferable.

Furthermore, polyols which forms the urethane prepolymer may bevinyl-(meth)acrylic acid ester-copolymerized polyols. As thevinyl-(meth)acrylic acid ester copolymerized-polyols, copolymers, forexample, produced from (meth)acrylic acid hydroxy alkyl ester such asbeta-hydroxyethyl(meth)acrylate etc. and (meth)acrylic acid derivativessuch as (meth)acrylic acid, methyl(meth)acrylate, ethyl(meth)acrylate,butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, etc. and vinyl group-containingcompounds can be exemplified.

A mixture of two or more of these polyether polyols, polyester polyolsand vinyl-(meth)acrylic acid ester-copolymerized polyols can be used assuch polyols.

These polyols preferably have a hydroxyl equivalent of 50-2,000, or anaverage molecular weight per hydroxyl group obtained by dividing anaverage molecular weight of the polyol by an average number of hydroxylgroups per molecule. When the hydroxyl equivalent is less than 50, aheat-cured coated layer formed from the plastisol composition containingthe fine powder of the acrylic resin added into the curable urethaneresin composition loses its flexibility due to an increase of itscrystallinity. When the equivalent is more than 2,000, the coated layerbecomes considerably deteriorated in its physical strength. Still morepreferable, the value of the hydroxyl equivalent is within the range of100-1,500.

As organic isocyanates which form the urethane prepolymer, at least onekind of monomer selected from aromatic diisocyanates, chain aliphaticdiisocyanates and cyclic aliphatic diisocyanates or an oligomer thereofis preferably used.

As aromatic diisocyanates, 2,4′-diphenylmethane diisocyanate,4,4′-diphenylmethane diisocyanate and mixtures thereof in any mixingratio; carbodiimide-modified diphenylmethane diisocyanate, polymerizeddiphenylmethane diisocyanate, urethane-modified diphenylmethanediisocyanate, modified diphenylmethane diisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate or mixtures thereof in anymixing ratio; xylylene diisocyanate, phenylene diisocyanate, naphthalenediisocyanate, triphenylmethane diisocyanate, toluidine diisocyanate,tetramethyl xylylene diisocyanate, diphenylsulfone diisocyanate, can beexemplified. Of which, tolylene diisocyanate, 2,4′-diphenylmethanediisocyanate, 4,4′-diphenylmethane diisocyanate andcarbodiimide-modified diphenylmethane diisocyanate are more preferable.As chain aliphatic diisocyanates, hexamethylene diisocyanate andtrimethyl hexamethylene diisocyanate can be exemplified. As cyclicaliphatic diisocyanates, hydrogenated diphenylmethane diisocyanate,isophorone diisocyanate and 3-isocyanatemethyl-3,5,5-triethylcyclohexylisocyanate can be exemplified. As organic isocyanates, amixture of two or more monomers of aromatic diisocyanates, chainaliphatic diisocyanates and cyclic aliphatic diisocyanates may beexemplified. As organic isocyanates, any isocyanate selected fromaromatic diisocyanates, chain aliphatic diisocyanates and cyclicaliphatic diisocyanates and mixtures thereof in any mixing ratio can beexemplified. As organic isocyanates, oligomers of organic isocyanatessuch as urethane-modified products, dimers, trimers,carbodiimaide-modified products, alophanate-modified products,urea-modified products, biuret-modified products, etc. may beexemplified.

When preparing the urethane prepolymer through polycondensation reactionof the polyols with the organic isocyanates, it is preferable to use, ina molar ratio, 1.2-2.0 isocyanate group equivalents of the organicisocyanates, preferably 1.5-2.0, with respect to one hydroxyl groupequivalent of the polyols. The isocyanate group equivalent or a valueobtained by dividing an average molecular weight of the urethaneprepolymer by a remaining average number of isocyanate group ispreferably within the range of 200-3,000. When the isocyanate equivalentis less than 200, a heat-cured coated layer formed from the plastisolcomposition containing the fine powder of the acrylic resin added intothe curable urethane resin composition becomes hard and brittle. Whenthe isocyanate equivalent is more than 3,000, the coated layer becomesdeteriorated in its adhesiveness. More preferable value of theisocyanate equivalent is within the range of 300-1,500. In addition, anNCO % in the urethane prepolymer (a ratio of the molecular weight of—NCO group to a molecular weight of the urethane prepolymer with respectto one —NCO group) is preferably within the range of 1.0-20%, morepreferably 2.0-10%.

An average molecular weight of the blocked urethane prepolymer ispreferably within the range of 1,000-500,000.

The curable urethane resin composition preferably contains 0.2-60 partsby weight of the polymer with respect to 100 parts by weight of theblocked urethane prepolymer, and more preferably 1.0-20 parts by weight.

Any known resin having various molecular weight and degree ofpolymerization can be used as the polymer as far as the resin can bedissolved into a solvent, a plasticizer, etc. which is added into thepolymer composition or the plastisol composition that contains thepolymer composition. The polymer is preferably at least one kindselected from acrylic resins, phenolic resins, epoxy resins, melamineresins, polyester resins, styrene resins, polyethylene resins, polyamideresins and polyurethane resins.

The polymer preferably has the average molecular weight within the rangeof 200-4,000,000 and a degree of polymerization within the range of1-40,000, more preferably the average molecular weight is within therange of 3,000-1,000,000.

As the acrylic resins, for example, (meth)acrylic ester copolymers suchas methyl (meth) acrylate, ethyl (meth)acrylate, butyl (meth) acrylate,2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, etc.can be exemplified. As acrylic resins, copolymers of (meth)acrylic acidester is also exemplified, and more precisely, copolymers of theaforementioned (meth)acrylic acid ester and at least one kind of vinylgroup-containing compound selected from unsaturated group-containingcarboxylic acids such as (meth)acrylic acid, maleic acid, etc., vinylesters, vinyl ethers such as vinyl methyl ether, vinyl butyl ether,etc., maleic acid esters such as diethylmaleate, dibutylmaleate, etc.,and fumaric acid esters such as diethyl fumaleate, dibuthylfumaleate,etc. are exemplified. The acrylic resins preferably has an averagemolecular weight of 2,000-4,000,000 and a degree of polymerization of20-40,000, more preferably 3,000-1,000,000 in the average molecularweight.

As the phenolic resins, novolak type phenol resins which is derived, forexample, from phenol, cresol, xylenol, etc. can be exemplified.

As the epoxy resins, ring-closed compounds obtained, for example,through reaction of a phenolic polynuclear compound withepichlorohydrin, more precisely, EPIKOTE (product name by JER), ARALDITE(product name by Ciba-Geigy Japan Ltd.) and EPICLON (product name byDIC), which are available in a series, can be exemplified.

The polymers such as acrylic resins, phenolic resins, epoxy resins, etc.are introduced into the curable urethane resin composition through, forexample, synthesizing those polymers in the blocked urethane prepolymer.Another method may be that the polymer is synthesized in advance in thepolyols, then the urethane prepolymer is synthesized, and then theprepolymer is blocked. Still another method may be that the polymer isadded and dissolved at the time of synthesis of the urethane prepolymer,and then blocked.

The urethane prepolymers can act as self-curing type resins which cancrosslink by themselves, so that the curable urethane resin compositioncan harden itself, even if no crosslinking agent exists.

The curable urethane resin composition may contain a crosslinking agentor a crosslinking catalyst.

As the crosslinking agent, same kind of polyols such as polyetherpolyols, polyester polyols, vinyl-(meth) acrylic acidester-copolymerized polyols, etc., all of which can form the urethaneprepolymer as mentioned above, are exemplified. Further, polyols such asaminopolyether polyols, etc., which are produced through addition ofalkylene oxides to lower alkylamines, can also be exemplified.Preferably, the hydroxyl equivalent of such polyols is within the rangeof 10-1,000.

As crosslinking agents, acid hydrazides such as oxalic acid dihydrazide,succinic acid dihydrazide, adipic acid dihydrazide, isophthalic aciddihydrazide, citric acid trihydrazide, maleic acid dihydrazide, etc.;aminoguanidines such as 1-amino-3-salicyl guanidine, triaminoguanidine,etc.; dicyandiamides such as dicyandiamide, n-butyldicyandiamide, etc.;guanyl ureas such as methylenebis guanyl urea, etc.; guanamines such asacetoguanamine, adipoguanamine, benzoguanamine, phthaloguanamine, etc.;melamines such as hexamethoxymethyl melamine, etc.; hydantoins such ashydantoin, 1-acetyl hydantoin, glycidyl hydantoin, etc.; acid imidessuch as acetylimide, phthalimide, succinimide, etc.; triazinering-containing compounds such as cyanuric acid, isocyanuric acid,melamine, methylolmelamine, TGIC (triglycidylisocyanulate),tris(2-hydroxyethyl)isocyanulate, etc. can be exemplified.

At least one kind selected from the above mentioned compounds ispreferably used as the crosslinking agent. Especially, aminopolyetherpolyols, which are addition products of alkylene oxides to loweralkylamines, are more preferable. Aminopolyether polyols having ahydroxyl equivalent of 10-400, which are addition products of alkyleneoxides to aliphatic alkyl amines are still more preferable.

The crosslinking agent is preferably added within the range of 0.5-1.2equivalents with respect to one —NCO group equivalent in the urethaneprepolymer.

When the polyols mentioned above is used as the crosslinking agent, acidhydrazides such as adipic acid dihydrazide, sebacic acid dihydrazide,etc.; dicyandiamides such as n-butyldicyanediamide, dicyanediamide,etc.; melamines such as hexamethoxymethyl melamine, etc.; acidimidessuch as succinimide, etc.; triazine ring-containing compounds such asisocyanuric acid, etc.; adducts of novolak phenols to either one ofdiethylenetriamine, triethylenetetramine and hexamethylenediamine; allof which act as a crosslinking aid or a potential curative agent, arepreferably added into the urethane resin composition in order to improvecuring characteristics. More specifically, AMICURE (registeredtrademark) PN-23, MY-24, PN-D, MY-D, PN-H (all of them are produced byAjinomoto Co. Inc.); FUJICURE (registered trademark) FXE-1000, FXR-1030(all of them are produced by Fujikasei Kogyo Co., Ltd.); adipic aciddihydrazide (ADH), strearic acid dihydrazide (SDH) (all of them areproduced by Nippon Hydrazine Co., Ltd.) can be exemplified.Aminoguanidines, guanyl ureas, guanamines or hydantoins may be used asthe crosslinking aid. Such crosslinking aids are added solely or in amixture of two or more of them. The total amount of the crosslinking aidto be added is preferably within the range of 0.2-1.2 equivalents withrespect to one equivalent of —NCO group in the urethane prepolymer.

These crosslinking agents and aids are optionally selected in view ofstorage stability, curing characteristics, etc. of the curable urethaneresin composition, or such properties as the melting point, the glasstransition temperature (Tg), etc. of the cured coated layer.

The curable urethane resin composition may contain an urethanizationcatalyst as the crosslinking catalyst, for example, a tin-containingcatalyst such as dibutyltin dilaurate, dibutyltin dimaleate,monobutyltin octoate, etc., because crosslinking and curingcharacteristics are further improved. The crosslinking catalyst may beadded in advance into the curable urethane resin composition or theheat-curable plastisol composition.

The heat-curable plastisol composition for coating of the presentinvention comprises the curable urethane resin composition and finepowder of an acrylic resin.

The heat-curable plastisol composition preferably contains 5-250 partsby weight of the curable urethane resin composition with respect to 100parts by weight of the fine powder of the acrylic resin. 80-0.5 parts byweight of a blocked urethane prepolymer may be contained with respect to100 parts by weight of the fine powder of the acrylic resin.

The fine powder of the acrylic resin is, for example, a copolymerizedacrylic resin made from (meth)acrylic esters and unsaturatedgroup-containing carboxylic acids, esters thereof or vinyl ether, oracrylic resins polymerized from (meth)acrylic esters. These acrylicresins preferably have an average molecular weight of 50,000-4,000,000and a glass transition temperature (Tg) of 20-120 degrees centigrade.The fine powder has preferably a particle size of 100 micrometer atmaximum, more preferably, not more than 10 micrometer. When the polymerin the curable urethane resin composition is an acrylic resin, the finepowder can be made from the same or different kind of material as thatof the polymer.

The heat curable plastisol composition for coating may contain a curingcatalyst, plasticizer, solvent, filler, stabilizer, flame retardant,foaming agent, etc. The curing catalysts are preferably organic tincompounds such as dibutyltin laurate, dibutyltin dimaleate, monobutyltinoctoate, etc., all of which are usually used as urethanizationcatalysts; or tertiary amines such as triethylamine, triethylenediamine,dimethylbenzylamine, etc., because these catalysts further improvecrosslinking and curing characteristics. These additives may be added inadvance in the curable urethane resin composition.

When the heat curable prastisol composition is applied and heated, theblocked urethane prepolymer in the composition is thermally split intourethane prepolymer and blocking agent. Terminal isocyanate groups ofthe urethane prepolymers are linked to each other through thecrosslinking agent. This reaction is repeated to at last form anetwork-like polymerized coated layer. Flexibility, elongationcharacteristics, tensile strength and adhesiveness of the coated layershow the same or higher level of that of a coated layer formed from apolyvinyl chloride resin-containing plastisol composition.

EXAMPLE

Hereunder, the curable urethane resin composition and the plastisolcomposition which contains the curable urethane resin composition andgives a coated layer of the present invention will be explained indetail.

Examples of the curable urethane resin composition and the plastisolcomposition are prepared as follows.

Propylene oxide adduct of glycerin as a polyether polyol, which is usedas the polyol, 2,4-tolylene diisocyanate as the organic isocyanate and(meth)acrylic ester polymer, which is an acrylic resin used as thepolymer, are charged and stirred at a temperature of 40-120 degreescentigrade, preferably 40-90 degrees centigrade, obtaining an urethaneprepolymer having a remaining isocyanate group at its end. In order toaccelerate the reaction, the organic tin compound such as dibutyltindilaurate, monobutyltin octoate, etc. or the tertiary amine such astriethylamine, triethylenediamine, dimethylbenzylamine, etc. can beused.

To the urethane prepolymer, methylethylketoxime as the blocking agent,and propylene oxide adduct of ethylenediamine as the crosslinking agent,are added and stirred at the same temperature. 50-100% of the terminalisocyanate group of the urethane prepolymer is reacted with the blockingagent, giving the blocked urethane prepolymer. The blocked urethaneprepolymer may have its terminal isocyanate group all protected by theblocking agent. The terminal isocyanate group may be partially blockedby the blocking agent or partially crosslinked in advance by thecrosslinking agent. In the following chemical equation [I], an exampleof the formation of the blocked urethane prepolymer (3) is shown inwhich all terminal isocyanate groups of the urethane prepolymer (1) areprotected by methylethylketoxime (2).

Through this reaction, the curable urethane resin composition containingthe acrylic resin uniformly dispersed in the blocked urethane prepolymeris obtained.

Into the curable urethane resin composition, fine powder of an acrylicresin, plasticizer, and calcium carbonate as the filler are admixed.When a compound which acts as a crosslinking agent or a crosslinking aidsuch as an acid hydrazide, a dicyandiamide, a melamine, an acid imideand a triazine ring-containing compound is added solely or in a mixtureof two or more of them and mixed uniformly, a heat curable plastisolcomposition having excellent curing characteristics and giving highercrosslinking density can be obtained.

The heat curable plastisol composition for coating is applied and heatedat about 110-130 degrees centigrade for about 30 min. Then, as shown inthe following chemical equation [II], the blocked urethane prepolymer(3) is decomposed and methylethylketoxime is thermally split,regenerating the terminal isocyanate group in the urethane prepolymer(1).

A crosslinking agent (4) named by N-oxypropylene-ethylenediamine, whichis a propyleneoxide adduct of ethylenediamine as an aminopolyetherpolyol, reacts with the terminal isocyanate groups to crosslink,yielding a partially crosslinked compound (5).

With respect to the crosslinked compound (5), crosslinking reactionfurther occurs sequentially, leading the compound (5) to at last astable network-like polymer, while containing the acrylic polymertherein, and forming a coated layer excellent in flexibility, elongationcharacteristics, tensile strength, flame resistance, adhesiveness, etc.When the aforementioned crosslinking agents such as adipic aciddihydrazide, isocyanuric acid are used, crosslinking is formed alike.

The curable urethane resin composition can also be prepared as follows.

Propylene oxide adduct of glycerine and an unsaturated compound such as(meth)acrylic ester are charged, synthesizing an acrylic polymer undernitrogen gas at 40-120 degrees centigrade using AIBN(2,2′-azobisisobutyronitrile) as a polymerization initiator. Then2,4-tolylene diisocyanate is charged and stirred at 40-120 degreescentigrade, preferably 40-90 degrees centigrade, obtaining the urethaneprepolymer having a remaining isocyanate group at its end. As is statedabove, an organic tin compound or a tertiary amine may be used as acatalyst to accelerate the reaction. Then the blocking agent such asmethylethylketoxime and the crosslinking agent such as propyleneoxideadduct of ethylenediamine, acid hydrazide, dicyandiamide, melamine, acidimide, a triazine ring-containing compound, etc. are added and stirredat the same temperature, producing the blocked urethane prepolymer andgiving the curable urethane resin composition. Hereunder, in preparatoryExamples 1-12, preparative procedures of the curable urethane resincomposition of the present invention are shown, and in ComparativeExamples 1-4, preparative procedures of a curable urethane resincomposition, which is outside the scope of the present invention, areshown.

Preparatory Example 1

Into a flask equipped with a stirrer, a thermometer and a nitrogen gasinlet, 174 parts by weight of 2,4-tolylene diisocyanate, 1,000 parts byweight of a polyether polyol having an average molecular weight of 3,000prepared through an addition of 50 equivalents of propylene oxide to oneequivalent of glycerine, 140 parts by weight of an acrylic polymerhaving an average molecular weight of 200,000 and Tg of 70 degreescentigrade, and 0.3 parts by weight of dibutyltin laurate were charged.The mixture was stirred under nitrogen atmosphere at an innertemperature of 45-90 degrees centigrade and reacted, synthesizing theurethane prepolymer. Next, to the reacted mixture, 78.3 parts by weight(90% equivalent) of methylethylketoxime as a blocking agent was droppedat 35-45 degrees centigrade and reacted to synthesize a blocked urethaneprepolymer. To this reacted mixture, 73 parts by weight of anaminopolyether polyol prepared through an addition of 4 equivalent ofpropylene oxide to one equivalent of ethylenediamine was added andstirred at 50-80 degrees centigrade. Reaction was allowed to continueuntil the infrared absorption peak at 2260 cm⁻¹ due to isocyanate groupwas not observed when infrared absorption spectrum of the reactionmixture was measured, obtaining the resin composition containing apartially-crosslinked blocked urethane prepolymer.

Preparatory Example 2

Into a flask with a stirrer, a thermometer and a nitrogen gas inlet,1,000 parts by weight of the same polyether polyol, which was used inPreparatory Example 1, having an average molecular weight of 3,000prepared through an addition of 50 equivalents of propylene oxide to oneequivalent of glycerine, 126 parts by weight of methylmethacrylate, 63parts by weight of n-butylmethacrylate and 126 parts by weight ofisobutylmethacrylate were charged, and 0.5 parts by weight of AIBN(2,2′-azoisobutyronitrile) was added to react at 40-120 degreescentigrade under nitrogen, synthesizing an acrylic resin as the polymer.Then 174 parts by weight of 2,4-tolylene diisocyanate, 0.3 parts byweight of dibutyltin dilaurate were further added to react at 40-90degrees centigrade, synthesizing a urethane prepolymer. Next, 78.3 partsby weight (90% equivalent) of methylethylketoxime was dropped at 40-50degrees centigrade to react to synthesize a blocked urethane prepolymer.To this reacted mixture, 73 parts by weight of aminopolyether polyolprepared through an addition of 4 equivalents of propylene oxide toethylene diamine was added and stirred at 50-80 degrees centigrade.Reaction was allowed to continue until the infrared absorption peak at2260 cm⁻¹ due to isocyanate group was not observed when infraredabsorption spectrum of the reaction mixture was measured, obtaining theresin composition containing a partially crosslinked blocked urethaneprepolymer.

Preparatory Example 3

To the urethane prepolymer containing the acrylic resin synthesized inPreparatory Example 1, 87 parts by weight (100% equivalent) ofmethylethylketoxime was dropped and reacted at 35-45 degrees centigrade.The reaction was allowed to continue until the infrared absorption peakat 2260 cm⁻¹ due to isocyanate group was not observed when infraredabsorption spectrum of the reaction mixture was measured. The curableurethane resin composition was obtained by adding 73 parts by weight ofan aminopolyether polyol prepared through addition of 4 equivalents ofpropylene oxide to ethylenediamine to the blocked urethane prepolymer.

Preparatory Example 4

To the urethane prepolymer containing the acrylic polymer synthesized inpreparatory Example 2, 87 parts by weight (100% equivalent) ofmethylethylketoxime was added and reacted at 35-45 degrees centigrade.The reaction was allowed to continue until the infrared absorption peakat 2260 cm⁻¹ due to isocyanate group was not observed when infraredabsorption spectrum of the reaction mixture was measured. The curableurethane resin composition was obtained by adding 73 parts by weight ofan aminopolyether polyol prepared through addition of 4 equivalents ofpropylene oxide to ethylenediamine to the blocked urethane prepolymer.

Preparatory Example 5

Except that a polyester polyol having an average molecular weight of3,000 prepared through ring-opening polymerization ofdelta-valerolactone and glycerine was used, in place of the polyetherpolyol prepared through addition of propylene oxide to glycerine, thecurable urethane resin composition was obtained through the sameprocedure as described in Preparatory Example 1.

Preparatory Example 6

Except that the polyester polyol having an average molecular weight of3,000 prepared through ring-opening polymerization ofdelta-valerolactone and glycerine was used, in place of the polyetherpolyol prepared through addition of propylene oxide to glycerine, thecurable urethane resin composition was obtained through the sameprocedure as described in Preparatory Example 2.

Preparatory Example 7

Except that dicyclohexylamine was used in place of methylethylketoxime,the curable urethane resin composition was obtained through the sameprocedure as described in Preparatory Example 1.

Preparatory Example 8

Except that dicyclohexylamine was used in place of methylethylketoxime,the curable urethane resin composition was obtained through the sameprocedure as described in Preparatory Example 2.

Preparatory Example 9

Except that a mixture of 2,4′-diphenylmethanediisocyanate and4,4′-diphenylmethanedisocyanate was used in place of2,4-tolylenediisocyanate, the curable urethane resin composition wasobtained through the same procedure as described in Preparatory Example1.

Preparatory Example 10

Except that a mixture of 2,4′-diphenylmethanediisocyanate and4,4′-diphenylmethanediisocyanate was used in place of2,4-tolylenedisocyanate, the curable urethane resin composition wasobtained through the same procedure as described in Preparatory Example2.

Preparatory Example 11

Except that aminopolyether polyol as the crosslinking agent was notused, the curable urethane resin composition was obtained through thesame procedure as described in Preparatory Example 3.

Preparatory Example 12

Except that aminopolyether polyol as the crosslinking agent was notused, the curable urethane resin composition was obtained through thesame procedure as described in Preparatory Example 4.

Comparative Preparatory Example 1

Except that the acrylic polymer used in Preparatory Example 1 was notused, the curable urethane resin composition was obtained through thesame procedure as described in Preparatory Example 1.

Comparative Preparatory Example 2

Except that the acrylic polymer used in Preparatory Example 3 was notused, the curable urethane resin composition was obtained through thesame procedure as described in Preparatory Example 3.

Comparative Preparatory Example 3

Except that the acrylic polymer and aminopolyether polyol as thecrosslinking agent used in Preparatory Example 3 were not used, thecurable urethane resin composition was prepared through the sameprocedure as described in Preparatory Example 3.

Comparative Preparatory Example 4

Except that the acrylic polymer used in Preparatory Example 5 was notused, the curable urethane resin composition was obtained through thesame procedure as described in Preparatory Example 5.

Examples 1-12 and Comparative Examples 1-4

10 parts by weight of the curable urethane resin composition prepared inPreparatory Examples 1-12 and Comparative Preparatory Examples 1-4, 24parts by weight of ZEON F-340 (trade name by Zeon Corporation) as finepowder of the acrylic resin, 36 parts by weight of diisononylphthalate(DINP) as a plasticizer, 40 parts by weight of CALSEEDS PL-10 (tradename by Konoshima Chemical Co., Ltd) as calcium carbonate of filler, 0.1parts by weight of S-CAT-1 (trade name by Sankyo Organic Chemical Co.,Ltd.), dibutyltin dilaurate (DBTL) as a crosslinking catalyst, 0.2 partsby weight of adipic acid dihydrazide (ADH) as a potentially curativeagent were charged into a mixer, kneaded and degassed to produce eachheat curable plastisol composition for coating corresponding to Examples1-12 and each plastisol composition corresponding to ComparativeExamples 1-4, respectively.

The heat curable plastisol compositions for coating corresponding toExamples 1-12 and Comparative Examples 1-4 were subjected to a storagestability test. In addition, these plastisol compositions were eachapplied on a cation coated steel plate, heated and cured. Thus obtainedcoated layers were subjected to chipping resistance test for measuringan adhesive strength, chipping resistance test after water immersion,elongation test at room temperature and −30 degrees centigrade,blistering test after moisture absorption.

(Storage Stability Test)

Viscosity at 25 degrees centigrade of each heat curable plastisol forcoating was measured using BH type viscometer. Next, each plastisolcomposition was stored for 10 days at 35 degrees centigrade, thenviscosity at 25 degrees centigrade was again measured. Assessment ofstorage stability was carried out by classifying results into twoclasses, that is when increasing rate of viscosity after storage wasless than 30% the result was designated by ◯; when not less than 30%, byX. The results were shown in Table 1.

(Chipping Resistance Test: Adhesion Strength Test)

Each heat curable prastisol composition for coating was applied so as tobe a square of 50-100 mm on a side and 0.5 mm thick on a cation coatedsteel substrate, then heat-treated at 120 degrees centigrade for 30minutes and then air-dried at room temperature for one day. The thusobtained test piece was tilted at an angle of 60 degree to the horizon,then a nut of 3 mm thick and 6 mm in diameter was dropped onto a circledarea of 4 cm in diameter within every 30 seconds. The procedure wasrepeated until the cation coated surface appeared by peeling, floatingor wearing of the coated layer. The total weight of nuts used until thecoated surface appeared was regarded as adhesion strength. Assessment ofadhesion strength was carried out by classifying results into twoclasses, that is when adhesive strength was not less than 40 kg, theresult was designated by ◯; while less than 40 kg, by X. The resultswere shown in Table 1.

(Chipping Resistance Test after Water Immersion: Adhesion Strength Test)

Each heat curable plastisol composition for coating was applied on acationic electrodeposition-coated steel plate having a square of 50-100mm on a side and 0.5 mm thick, heat-treated at 120 degrees centigradefor 30 minutes and then air-dried at room temperature for one day. Thethus obtained samples were immersed into water at 40 degrees centigradefor 14 days. After picked them out and wiped, they were air-dried at aroom temperature for one day, obtaining test pieces. Adhesion strengthtest after water immersion was carried out in the similar way asdescribed in the above mentioned Adhesion Strength Test. Assessment wascarried out by classifying results into two classes, that is whenadhesion strength was not less than 20 kg, the result was designated by◯; while less than 20 kg, by X. The results were shown in Table 1.

(Elongation Test at 25 Degrees Centigrade)

Each heat curable plastisol composition for coating was applied so as tobe a thickness of 1 mm on a glass plate, then heat-treated at 120degrees centigrade for 30 minutes and then air-dried at a roomtemperature for one day, and then punched out to obtain a test piece.Elongation of the test piece was measured under a constanttemperature-and-humidity atmosphere at the room temperature usingRheometer (Model: CR-2000D, or CR-300 (by Sun Seientifie Co., Ltd.)).Assessment was carried out by classifying the results into threeclasses, that is when elongation was not less than 300%, the result wasdesignated by ◯; while elongation was within the range of 250-299%, byΔ; and less than 250%, by X. The results were shown in Table 1.

(Elongation Test at −30 Degrees Centigrade)

Test pieces were prepared according to the same procedure as inElongation Test at 25 degrees centigrade. Then elongation was measuredin an atmosphere at −30 degrees centigrade using the same Rheometer.Elongation was assessed by classifying the results into two classes,that is when elongation is not less than 75%, the result was designatedby ◯, while less than 75%, by X. Results were shown in Table 1.

(Blistering Test after Moisture Absorption)

Each heat curable plastisol composition for coating was applied so as tobe a square of 50 mm by 100 mm and 0.5 mm thick on a cationicelectrodeposition-coated steel plate, obtaining a test piece. The testpiece was exposed to an atmosphere at a humidity of 80% and at 30degrees centigrade for one day and preheated at 110 degrees centigradefor 10 minutes and then heat-treated at 140 degrees centigrade for 30minutes. The thus obtained coated layer was examined with the naked eyesto determine whether or not foaming or blistering occurred on thesurface. Assessment was carried out by classifying the results into twoclasses, that is when no foaming or blistering was observed, the resultwas designated by ◯; while foaming or blistering was observed, by X.Results were shown in Table 1. TABLE 1 Example 1 2 3 4 5 6 7 8Compounding Urethane Prep. 1 10 (parts by weight) resin Ex. 2 10composition 3 10 4 10 5 10 6 10 7 10 8 10 9 10 11 12 Comp. 1 Prep. 2 Ex.3 4 Fine Zeon 24 24 24 24 24 24 24 24 powder F-340 of acrylic resinPlasticizer DINP 36 36 36 36 36 36 36 36 Filler Calseeds 40 40 40 40 4040 40 40 p110 Crosslinking DBTL 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 catalystCrosslinking ADH 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 aid Physical StorageViscosity 18 18 22 23 25 28 28 25 Properties stability increase (%)Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Chipping Total 54 62 48 50 44 48 42 44 weightof nuts (kg) Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Chipping Total 36 37 28 30 26 2623 26 after weight of immersion nuts (kg) Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯Elongation Elongation 309 305 313 317 290 294 300 303 at (%) 25 deg. C.Evaluation ◯ ◯ ◯ ◯ Δ Δ ◯ ◯ Elongation Elongation 106 109 110 116 89 9385 91 at (%) −30 deg. C. Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ BlisteringBlistering No No No No No No No No Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Comp.Example Example 9 10 11 12 1 2 3 4 Compounding Urethane Prep. 1 (partsby weight) resin Ex. 2 composition 3 4 5 6 7 8 9 10 10 10 11 10 12 10Comp. 1 10 Prep. 2 10 Ex. 3 10 4 10 Fine Zeon 24 24 24 24 24 24 24 24powder F-340 of acrylic resin Plasticizer DINP 36 36 36 36 36 36 36 36Filler Calseeds 40 40 40 40 40 40 40 40 p110 Crosslinking DBTL 0.1 0.10.1 0.1 0.1 0.1 0.1 0.1 catalyst Crosslinking ADH 0.2 0.2 0.2 0.2 0.20.2 0.2 0.2 aid Physical Storage Viscosity 20 21 12 10 22 22 18 25Properties stability increase (%) Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ChippingTotal 51 55 41 40 40 34 14 31 weight of nuts (kg) Evaluation ◯ ◯ ◯ ◯ ◯ XX X Chipping Total 29 34 26 24 25 19 4 16 after weight of immersion nuts(kg) Evaluation ◯ ◯ ◯ ◯ ◯ X X X Elongation Elongation 300 300 280 270220 220 210 220 at (%) 25 deg. C. Evaluation ◯ ◯ Δ Δ X X X X ElongationElongation 101 100 78 81 60 60 70 61 at (%) −30 deg. C. Evaluation ◯ ◯ ◯◯ X X X X Blistering Blistering No No No No No No No Yes Evaluation ◯ ◯◯ ◯ ◯ ◯ ◯ X

From Table 1, the heat curable plastisol composition for coating ofExamples 1-12 all show an excellent storage stability, and the heatedand cured coating layers thereof all have an excellent adhesivestrength, elongation characteristics and blistering after moistureabsorption. On the contrary, the heated and cured coating layer of theplastisol composition of Comparative Examples 1-4 all show poor adhesionstrength, elongation characteristics and blistering after moistureabsorption.

Next, examples of other curable urethane resin compositions of thepresent invention will be shown in Preparatory Examples 13-20. Examplesof other curable urethane resin compositions outside the scope of thepresent invention will be shown in Comparative Preparatory Examples 5-10hereunder.

Preparatory Example 13

Into a flask equipped with a stirrer, a thermometer and a nitrogen gasinlet, 174 parts by weight of 2,4-tolylene diisocyanate, 1,000 parts byweight of polyether polyol having an average molecular weight of 3,000prepared through addition of 50 equivalents of propylene oxide to oneequivalent of glycerine, 140 parts by weight of an acrylic resin havingan average molecular weight of 200,000, 0.3 parts by weight ofdibutyltin dilaurate were charged under nitrogen gas and stirred toreact at internal temperature of 40-90 degrees centigrade, synthesizingan urethane prepolymer. Next, to the thus obtained mixture, 78.3 partsby weight (90% equivalent) of methylethyl ketoxime, a blocking agent,was dropped to react at 40-50 degrees centigrade, synthesizing theblocked urethane prepolymer. Then to the reacted mixture, 73 parts byweight of aminopolyether polyol prepared through addition of 4equivalents of propylene oxide to one equivalent of ethylenediamine wasadded and stirred at 50-80 degrees centigrade. The reaction was allowedto continue until the infrared absorption peak of 2260 cm⁻¹ due toisocyanate group was not observed when infrared absorption spectrum ofthe reaction mixture was measured, obtaining the resin compositioncontaining a partially-crosslinked blocked urethane prepolymer.

Preparatory Example 14

Into a flask equipped with a stirrer, a thermometer and a nitrogen gasinlet, 1,000 parts by weight of the same polyether polyol having anaverage molecular weight of 3,000 prepared through addition of 50equivalents of propylene oxide to one equivalent of glycerine asdescribed in Preparatory Example 13, 126 parts by weight ofmethylmethacrylate, 63 parts by weight of n-butylmethacrylate, 126 partsby weight of isobutylmethacrylate were charged and 0.5 parts by weightof AIBN (2,2′-azoisobutyronitrile) was added to react at 40-120 degreescentigrade under nitrogen gas, synthesizing an acrylic resin as thepolymer. Then 174 parts by weight of 2,4-tolylene diisocyanate and 0.3parts by weight of dibutyltin dilaurate were charged to react at 40-90degrees centigrade, synthesizing an urethane prepolymer. Next, 78.3parts by weight (90% equivalent) of methylethylketoxime was dropped toreact at 40-50 degrees centigrade, synthesizing the blocked urethaneprepolymer. To the thus obtained reaction mixture, 73 parts by weight ofaminopolyether polyol prepared through addition of 4 equivalents ofpropylene oxide to ethylenediamine was added and stirred at 50-80degrees centigrade. The reaction was allowed to continue until theinfrared absorption peak of 2260 cm⁻¹ due to isocyanate group was notobserved when infrared absorption spectrum of the reaction mixture wasmeasured, obtaining the resin composition containing apartially-crosslinked blocked urethane prepolymer.

Preparatory Example 15

Except that 172.2 parts by weight (95% equivalent) of dicyclohexylaminewas dropped in place of methylethylketoxime used in Preparatory Example13, to react at 40-45 degrees centigrade and synthesize the blockedurethane prepolymer, the curable urethane resin composition was obtainedthrough the same procedure as described in Preparatory Example 13.

Preparatory Example 16

Except that polyester polyol having an average molecular weight of 3,000prepared through ring-opening polymerization of glycerine anddelta-valerolactone was used in place of polyether polyol preparedthrough addition of propylene oxide to glycerine used in PreparatoryExample 13, the curable urethane resin composition was obtained throughthe same procedure as described in Preparatory Example 13.

Preparatory Example 17

Except that 172.2 parts (95% equivalent) by weight of dicyclohexylaminewas added in place of methylethylketoxime in Preparatory Example 13, toreact at 40-45 degrees centigrade and synthesize the blocked urethaneprepolymer, the curable urethane resin composition was obtained throughthe same procedure as described in Preparatory Example 13.

Preparatory Example 18

Except that a mixture of 2,4′-diphenylmethane diisocyanate and4,4′-diphenylmethane diisocyanate was used in place of2,4-tolylenediisocyanate used in Preparatory Example 13, the curableurethane resin composition was obtained through the same procedure asdescribed in Preparatory Example 13.

Preparatory Example 19

Except that 172.2 parts by weight (95% equivalent) of dicyclohexylaminewas added in place of methylethylketoxime used in Preparatory Example18, to react at 40-45 degrees centigrade and synthesize the blockedurethane prepolymer, the curable urethane resin composition was obtainedthrough the same procedure as described in Preparatory Example 18.

Preparatory Example 20

Except that a novolak type phenol resin (average molecular weight:200-4,000) was used in place of the acrylic resin used in PreparatoryExample 13, the curable urethane resin composition was obtained throughthe same procedure as described in Preparatory Example 13.

Preparatory Example 21

Except that an epoxy resin (average molecular weight: 400-2,500) wasused in place of the acrylic resin used in Preparatory Example 13, and apolyfunctional polyol (polyglycerine: average molecular weight1,300-1,500) was used in place of aminopolyether polyol used inPreparatory Example 13, the urethane resin composition was obtainedthrough the same procedure as described in Preparatory Example 13.

The curable urethane resin compositions obtained in Preparatory Examples13-21 were evaluated as an urethane resin composition by adding as shownin Table 2, adipic acid dihydrazide (ADH) as acid hydrazides,dicyandiamides, hexamethoxymethylmelamine as melamines, succinimide asacid imides and isocyanuric acid as triazine ring-containing compounds,solely or a mixture of two or more of them, and also by addingdibutyltin dilaurate as crosslinking catalyst.

Comparative Preparatory Example 5

Except that the acrylic resin used in Preparatory Example 13 was notused, the urethane resin composition was obtained through the sameprocedure as described in Preparatory Example 13.

Comparative Preparatory Example 6

Except that aminopolyether polyol prepared through addition of 4equivalents of propylene oxide to one equivalent of ethylenediamine usedin Preparatory Example 13 was not used, the urethane resin compositionwas obtained through the same procedure as described in PreparatoryExample 13.

Comparative Preparatory Example 7

The urethane resin composition in Comparative Preparatory Example 7 didnot contain the crosslinking aid added to the curable urethane resincomposition in Preparatory Example 13.

Comparative Preparatory Example 8

The urethane resin composition in Comparative Preparatory Example 8 didnot contain the curing catalyst (dibutyltin dilaurate) added to thecurable urethane resin composition in Preparatory example 13.

Comparative Preparatory Example 9

The urethane resin composition in Comparative Preparatory Example 9 wasobtained, as shown in Table 2, by adding adipic acid dihydrazide as acrosslinking aid to the urethane resin composition obtained inComparative Preparatory Example 6 and did not contain aminopolyetherpolyol.

Comparative Preparatory Example 10

The urethane resin composition in Comparative Preparatory Example 10 didnot contain the curing catalyst (dibutyltin dilaurate) to be added intothe urethane resin composition which did not contain aminopolyetherpolyol obtained in Preparatory Example 6.

Examples 13-21 and Comparative Examples 5-10

15 parts by weight of curable urethane resin composition obtained inPreparatory Examples 13-21 or urethane resin composition obtained inComparative Preparatory Examples 5-10, 24 parts by weight of core/shelltype fine powder of an acrylic resin having an average molecular weightof 700,000 and an average particle size of 0.5 micro meter, 35 parts byweight of diisononylphtalate (DINP) as the plasticizer, 26 parts byweight of NEOLIGHT SP (trade name, produced by Takehara Kagaku KogyoCo., Ltd), calcium carbonate as a filler, were charged into a mixer,mixed for 30 minutes and degassed, obtaining heat curable plastisolcompositions for coating of each Examples 13-21 and plastisolcompositions of each Comparative Examples 5-10, respectively.

Plastisol Compositions of Examples 13-21 and Comparative examples 5-10were subjected to storage stability test. These plastisol compositionswere applied on a cationic electrodeposition-coated steel platesubstrate, heated and cured, forming coated layers. The coated layerswere subjected to chipping resistance test, chipping resistance testafter water immersion, adhesion shearing test and blistering test aftermoisture absorption.

(Storage Stability Test)

Viscosity at 25 degrees centigrade of each plastisol composition ofExamples 13-21 and Comparative Examples 5-10 was measured using BH typeviscometer. Next, each plastisol was stored for 10 days at 40 degreescentigrade, then viscosity at 25 degrees centigrade was again measured.Storage stability was assessed by grouping the results into two classes,that is when increasing rate of viscosity after storage was less than30%, the result was designated by ◯; when not less than 30%, by X.Results are shown in Table 2.

(Chipping Resistance Test: Adhesion Strength Test)

Each plastisol composition was applied so as to be a square of 50-100 mmon a side and 0.4 mm thick after drying on a cationicelectrodeposition-coated steel plate substrate, heat-treated at 120degrees centigrade for 30 minutes and then air-dried at room temperaturefor one day, obtaining a test piece. The test piece was tilted at 60degree to the horizon and a pipe having 20 mm in inner diameter and 2 mlong was vertically mounted on the coating layer. Dropping of a M-4 nut(Japanese Industrial Standard) from the upper end of the pipe wascontinued until the steel plate substrate appeared, measuring the totalweight of the nuts used. Chipping resistance was assessed by groupingthe results into two classes, that is when the total weight is not lessthan 35 kg, the result was designated by ◯; when less than 35 kg, by X.Results are shown in Table 2.

(Chipping Resistance Test after Water Immersion: Adhesion Strength Test)

Test pieces of each plastisol composition were prepared in the samemanner as described in the chipping resistance test and air-dried atroom temperature for one day. These test pieces were immersed into waterat 40 degrees centigrade for 14 days, and picked out and wiped, and thenair-dried at room temperature for one day. Chipping resistance testafter water immersion was carried out in the same manner as described inthe above mentioned chipping resistance test, measuring the total weightof nuts used until the steel plate substrate appeared. Chippingresistance was assessed by grouping the results into two classes, thatis when the total weight is not less than 20 kg, the result wasdesignated by ◯; when less than 20 kg, by X. Results are shown in Table2.

(Adhesion Shearing Test)

Each plastisol composition was applied on an edge portions of twocationic electrodeposition-coated steel plates having 5 mm width, and aspacer was inserted so as to make the volume of coated layer become 25mm×25 mm×3 mm thick, then heat-treated at 130 degrees sentigrade for 30minutes, and then air-dried at room temperature for one day, obtaining atest piece. The thus obtained test piece was attached to both ends of atensile shear tester and stretched at a stretching speed of 50 mm/min.Tensile strength was measured, and condition of fracture surface wasobserved for determining whether the fracture surface was cohesivefailure (CF) or interfacial failure (AF). Values in the interfacialfailure box indicate the ratio of area of adhesive failure surface inthe bonding area of 25 mm×25 mm. Results are shown in Table 2.

(Blistering Test after Moisture Absorption)

Each plastisol composition was applied so as to be a square of 50-100 mmon a side and 0.4 mm thick after drying, exposed to an atmosphere at ahumidity of 80% and at 30 degrees centigrade for one day, preheated at110 degrees centigrade for 10 minutes, and then heat-treated at 140degrees centigrade for 30 minutes. The surface of the resulted coatedlayer was examined whether or not foaming or blistering occurred on thesurface. Blistering was assessed by grouping results into two classes,that is when there was no foaming or blistering, it was designated by ◯,when foaming or blistering was observed, by X. Results are shown inTable 2. TABLE 2 Example 13 14 15 16 17 18 19 20 Compounding UrethanePrep. 13 15 (parts by weight) resin Ex. 14 15 composition 15 15 16 15 1715 18 15 19 15 20 15 21 Comp. 5 Prep. 6 Ex. 7 8 9 10 Polymer Add Add AddAdd Add Add Add Add (acrylic resin) Crosslinking Add Add Add Add Add AddAdd Add agent (aminopoly- ether polyol) Fine Zeon 24 24 24 24 24 24 2424 powder F-340 of acrylic resin Plasticizer DINP 35 35 35 35 35 35 3535 Filler Neolight SP 26 26 26 26 26 26 26 26 Crosslinking ADH 0.1 0.20.2 0.2 0.1 0.2 0.2 aid dicyanamide 0.3 0.3 Hexamethoxy 0.2 0.3 methyl-melamine Succinimido 0.4 Isocyanuric 0.3 0.3 0.3 acid Crosslinking DBTL0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 catalyst Physical StorageEvaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Properties stability Chipping Total weight 4061 58 53 49 58 55 53 of nuts (Kg) Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ChippingTotal weight 23 34 30 28 23 32 31 30 after of nuts (Kg) immersionEvaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Adhesion Condition CF CF CF CF CF CF CF CFShearing of fracture Test surface Ratio of area 0 0 0 0 0 0 0 0 ofadhesive failure surface (%) Blistering Blistering No No No No No No NoNo Evaluation ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Example Comparative Example 21 5 6 7 8 910 Compounding Urethane Prep. 13 (parts by weight) resin Ex. 14composition 15 16 17 18 19 20 21 15 Comp. 5 15 Prep. 6 15 Ex. 7 15 8 159 15 10 15 Polymer Add None Add Add Add Add Add (acrylic resin)Crosslinking Add Add None Add Add None None agent (aminopoly- etherpolyol) Fine Zeon 24 24 24 24 24 24 24 powder F-340 of acrylic resinPlasticizer DINP 35 35 35 35 35 35 35 Filler Neolight SP 26 26 26 26 2626 26 Crosslinking ADH 0.2 0.5 aid dicyanamide Hexamethoxy methyl-melamine Succinimido Isocyanuric 0.3 0.3 0.3 0.3 0.3 acid CrosslinkingDBTL 0.03 0.03 0.03 0.03 0.03 catalyst Physical Storage Evaluation ◯ ◯ ◯◯ ◯ ◯ ◯ Properties stability Chipping Total weight 56 38 Non- 35 Non- 18Non- of nuts (Kg) curable curable curable Evaluation ◯ ◯ ◯ X ChippingTotal weight 28 14 21 6 after of nuts (Kg) immersion Evaluation ◯ X ◯ XAdhesion Condition CF CF CF AF Shearing of fracture Test surface Ratioof area 0 4 0 67 of adhesive failure surface (%) Blistering BlisteringNo Yes Little Yes Evaluation ◯ X X X

As shown in table 2, the plastisol composition of Examples 13-21 wereexcellent in storage stability and the heated and cured coated layersthereof were excellent in adhesiveness, elongation characteristics andblistering after moisture absorption. On the contrary, as shown inComparative Examples 6, 8 and 10, curability was so poor that evaluationof solid state properties could not be carried out. In ComparativeExamples 5, 7 and 9, curability was not so bad but blistering wasobserved. In Comparative Example 9, chipping resistance after waterimmersion was very poor.

INDUSTRIAL APPLICABILITY

As precisely explained above, the curable urethane resin composition ofthe present invention can be used for heat curable plastisol compositionfor coating. Terminal isocyanate groups of the urethane prepolymercrosslink to each other to form a network-like polymer, in which theacrylic polymer is contained.

Therefore, the heat curable plastisol composition comprising the curableurethane resin composition and the fine powder of the acrylic resin canform a coated layer firmly adhering to a coated metal surface,especially to a cationic electrodeposition-coated surface, with a heattreatment at a comparatively lower temperature for a short period oftime. Furthermore, the coated layer is excellent in flexibility,elongation characteristics, tensile strength, adhesive strength anddurability. In addition, the heat curable plastisol composition forcoating has excellent storage stability.

The heat curable plastisol composition for coating can be used, in placeof a polyvinylchloride resin-containing plastisol composition, as achipping resistant paint, coating paint, sealing material, which areused for rust prevention for vehicle bodies, buffers against scatteringstone, waterproof of joint sealant, etc in auto industry. Further,conventional coating apparatuses, heat-treating apparatuses, etc. forpolyvinylchloride resin-containing plastisol composition can be used asthey are for the heat curable plastisol composition for coating of thepresent invention.

1. A curable urethane resin composition comprising: a blocked urethaneprepolymer which is prepared through condensation polymerization of apolyol and an organic isocyanate and has a terminal isocyanate groupprotected by a blocking agent; and a polymer dispersed or dissolved inthe blocked urethane prepolymer.
 2. The curable urethane resincomposition according to claim 1, wherein the resin composition furthercomprising a crosslinking agent which performs crosslinking reactionwith the terminal isocyanate group of the urethane prepolymer formedthrough deblocking of the blocked urethane prepolymer, the crosslinkingagent performing the crosslinking reaction to make the prepolymer form ahigher molecule while containing the polymer therein.
 3. The curableurethane resin composition according to claim 1, wherein a weight ratioof the blocked urethane prepolymer to the polymer is within the range of100:0.2-60.
 4. The curable urethane resin composition according to claim1, wherein at least one kind of agent selected from oximes, secondaryamines, phenols, alcohols and hydroxyl group-containing (meth)acrylicacid esters is used as the blocking agent.
 5. The curable urethane resincomposition according to claim 1, wherein at least one kind of polyolhaving a hydroxyl equivalent of 50-2,000 selected from polyetherpolyols, polyester polyols and vinyl-(meth)acrylic acid estercopolymerized polyols is used as the polyol.
 6. The curable urethaneresin composition according to claim 1, wherein at least one kind ofmonomer selected from aromatic diisocyanates, chain aliphaticdiisocyanates and cyclic aliphatic diisocyanates; and oligomers thereof;is used as the organic isocyanate.
 7. The curable urethane resincomposition according to claim 2, wherein at least one kind of agentselected from polyols which has a hydroxyl equivalent of 10-1,000 and isat least either one of aminopolyether polyols prepared through additionof lower alkylamine to alkylene oxide, polyether polyols, polyesterpolyols and vinyl-(meth)acrylic acid ester copolymerized polyols; acidhydrazides; aminoguanidines; dicyandiamides; guanyl ureas; guanamines;melamines; hydantoins; acid imides and triazine ring-containingcompounds: is used as the crosslinking agent.
 8. The curable urethaneresin composition according to claim 1, wherein the polymer is acrylicresins, phenolic resins, epoxy resins, melamine resins, polyesterresins, styrene resins, polyethylene resins, polyamide resins orpolyurethane resins.
 9. The curable urethane resin composition accordingto claim 1, wherein the polymer is an acrylic resin of a copolymer of a(meth)acrylic acid ester and at least one kind of vinyl group-containingcompound selected from an unsaturated group-containing carboxylic acid,a vinyl ester, a vinyl ether, a maleic acid ester and a fumaric acidester, or of a polymer of a (meth)acrylic acid ester.
 10. The curableurethane resin composition according to claim 1, wherein the polymer hasan average molecular weight of 200-4,000,000 and a degree ofpolymerization of 1-40,000.
 11. The curable urethane resin compositionaccording to claim 1, wherein the blocked urethane prepolymer has anaverage molecular weight of 1,000-500,000.
 12. A heat curable plastisolcomposition for coating comprising: a curable urethane resin compositioncomprising a blocked urethane prepolymer which is prepared throughcondensation-polymerization of a polyol and an organic isocyanate andhas a terminal isocyanate group protected by a blocking agent, and apolymer dispersed or dissolved in the blocked urethane prepolymer; andfine powder of an acrylic resin.
 13. The heat curable plastisolcomposition for coating according to claim 12, wherein the heat curableplastisol composition further comprising a crosslinking agent whichperforms crosslinking reaction with the terminal isocyanate group of theurethane prepolymer formed through deblocking of the blocked urethaneprepolymer, the crosslinking agent performing the crosslinking reactionto make the prepolymer form a higher molecule while containing thepolymer therein.
 14. The heat curable plastisol composition for coatingaccording to claim 12, wherein the blocked urethane prepolymer has anaverage molecular weight of 1,000-500,000 and the polymer has an averagemolecular weight of 200-4,000,000 and a degree of polymerization of1-40,000.